A printing device generally prints an image on a piece of paper upon receipt of an instruction. Firstly, the image data is analyzed into three basic colors (Red, Green and Blue) and is later converted into C, M, Y, K printing colors by the Color Management Module so that the Cyan, Magenta, Yellow and K colors are printed on the paper in an overlapping manner. The final product (the printout) therefore has CMYK colors.
Referring to FIG. 1, in the conventional printing process, the image data 6 can be divided into a foreground data 2 and a background data 4 which are respectively converted by the CMM into C, M, Y, K printing colors 8 such that the foreground data 2 is formed by a Cyan data 202 (gray value 30), a Magenta data 204 (gray value 30), a Yellow data 206 (gray value 30) and a K data 208 (gray value 200) while the background data 4 is formed by a Cyan data 402 (gray value 200), a Magenta data 404 (gray value 100), a Yellow data 406 (gray value 50) and a K data 408 (gray value 200).
In order to print out the foreground 1004 of an image 10, a predetermined color (K in the drawing) is selected from the printing colors 8 such that the Cyan data 202, 402 of the foreground and background are converted into the Cyan data group 602, the Magenta data 204, 404 of the foreground and background into the Magenta data group 604, the Yellow data 206, 406 of the foreground and background into the Yellow data group 606, the K data 208, 408 22 of the foreground and background into the K data group 608.
The Cyan data group 602, the Magenta data group 604, the Yellow data group 606 and the K data group 608 are later printed one above another in the overlapping manner in order to achieve the image 10 (the printout).
As shown in FIG. 1, a shadow 1002 or silhouette may appear around the peripheral portion of the foreground 1004 of the printout 10 when there is misregistration due to shifting of paper or the color-applying plate during overprinting operation of the Cyan data group 602, the Magenta data group 604, the Yellow data group 606 and the K data group 608 one above another.
FIG. 2 illustrates how a conventional printing technique prints an image data 6 into a printout 10. The image data 6 can be divided into a foreground 2 and a background 4. When the image data 6 is printed out as illustrated in FIG. 1, there may appear a shadow 1002 or a silhouette around the peripheral portion of the foreground 1004 of the printout 10 due to shifting of the paper or the color-applying plate.
To eliminate the aforesaid drawback caused by the conventional printing technique, trapping is usually done (printing small areas of overlapping colors where the foreground and background meet) to compensate the misregistration.